Modified X-Type Molecular Sieve for p-Xylene Mass Transfer

The patent introduces mesopores (2-50 nm) and macropores (>50 nm) into the X-type molecular sieve structure through hydrothermal treatment with organic ammonium salts as structure-directing agents. This hierarchical pore structure maintains the micropore volume for selective adsorption while adding larger pores for improved mass transfer and accessibility of aromatic hydrocarbon isomers to active sites.

The patent transitions from a traditional single-scale micropore structure to a hierarchical multi-scale pore structure by incorporating mesopores and macropores alongside micropores. This dimensional expansion of pore size distribution enables simultaneous optimization of selectivity (via micropores) and mass transfer (via meso- and macropores).

The patent creates a hierarchical pore structure where micropores provide high adsorption capacity through increased micropore volume, while interconnected mesopores and macropores provide efficient diffusion pathways. The mesopores act as transport channels that facilitate rapid movement of aromatic hydrocarbons to micropore regions, resolving the trade-off between capacity and transfer efficiency.

The patent implements a nested pore structure where mesopores and macropores serve as outer transport channels that nest around and provide access to the inner micropore regions. This nested architecture allows large pores to facilitate mass transfer while small micropores provide adsorption capacity, with each scale serving its optimal function.